1. Field of the Invention
The present invention relates to a semiconductor device in which a quantum well layer is employed and a method of manufacturing the same. More specifically, the invention relates to a semiconductor device having a three-terminal device structure in which each of a source electrode, a drain electrode and a gate electrode is provided, and a method of manufacturing the same.
2. Description of the Related Art
A semiconductor device which shows negative differential conductance (NDC) can be broadly applied to different kinds of fields as a functional device. Among such devices, with regard to a two-terminal device, with advances in ultra-thin-film crystal growth technique such as a molecular beam epitaxy method, a metal organic chemical vapor deposition method or the like, a resonant-tunneling diode which shows excellent characteristics making use of resonant-tunneling effect in a quantum well has been easily manufactured.
On the other hand, a three-terminal device which can control the negative differential conductance characteristic in a third electrode has greater flexibility than the two-terminal device.
Examples of three-terminal devices include, for example, a three-terminal device in which a third electrode is formed in a quantum well, which is constituted with ultra thin films, of a vertical resonant-tunneling diode (K. Maezawa and T. Mizutani, Jpn. J. Appl. Phys. 32 L42, 1993), a quasi-three-terminal device in which a resonant-tunneling diode and a three-terminal transistor are formed on the same substrate (K. J. Chen, K. Maezawa and Y Yamamoto, IEEE Electron Device, Lett. 17 127, 1996) and a three-terminal device in which real-space transfer of hot-electrons is used (C.-T. Liu, S. Luryi. P., A.Garbinski, A. Y. Cho, and D. L. Sivico, IEEE Trans, Electron Device 38 2417, 1991). In addition, a three-terminal device in which a third electrode is provided in an interband diode (T. Uemura and T.Baba, Jpn. J. Appl. Phys. 32 L207, 1994) is developed.
However, these three-terminal devices have the following problems. For the three-terminal device in which the third electrode is formed in the quantum well, which is constituted with the ultra thin films, of the vertical resonant-tunneling diode, there exists a problem such that its manufacturing process is complicated and resistance in the third electrode becomes large. With the quasi-three-terminal device where the resonant-tunneling diode and the three-terminal transistor are formed on the same substrate, the manufacturing process is complicated and difficult. Further, in the three-terminal device in which a third electrode is provided in an interband tunnel diode, a complicated and difficult manufacturing process is required. In the three-terminal device in which real-space transfer of hot-electrons is utilized, there is a problem such that large electric field needs to be applied in order to increase the temperature of electrons. Thus, it is difficult to control the characteristic of the three-terminal device.
The present invention has been achieved in view of the above problems. It is an object of the invention to provide a semiconductor device which shows excellent negative differential conductance or negative transconductance and is manufactured without a complicated manufacturing process, and a method of manufacturing the same.
The semiconductor device of the invention includes a conduction region, a floating region which is electrically separated from the conduction region, a quantum well layer disposed between the conduction region and the floating region, a source electrode and a drain electrode each of which is electrically connected to the conduction region, and a gate electrode provided in a position opposite from the quantum well layer in the floating region. Furthermore, in the semiconductor device of the invention, drain current characteristics show negative differential conductance when changing the drain voltage relative to a predetermined gate voltage.
Moreover, the method of manufacturing a semiconductor device of the invention includes a first step for sequentially forming the conduction region, the quantum well layer, and the floating region on a substrate, and a second step for shaping the floating region by selectively removing a region, in which the source electrode and the drain electrode will be formed, by an etching agent including citric acid or mixing chlorine-based and fluorine-based species.
With the semiconductor device of the present invention, as varying the drain voltage relative to the gate voltage, transfer of carriers occurs due to resonant-tunneling effect between the conduction region and the floating region through the quantum well layer. Accordingly, negative differential conductance occurs in the drain current characteristics.
With the method of manufacturing a semiconductor device of the present invention, the conduction region, the quantum well layer and the floating region are formed on the substrate in this order, and the region where the source electrode and the drain electrode will be formed is selectively removed by an etching agent including critic acid or mixing chlorine-based and fluorine-based species.
Other and further objects, features and advantages of the invention will appear more fully from the following description.